A rotary electric machine is widely utilized as a power source for various devices. A common permanent-magnet AC rotary electric machine is configured to include a stator having a coil and a rotor having permanent magnets that serve as magnetic poles. In an inner-rotor rotary electric machine, in many cases, a stator core around which the coil is wound is formed by stacking a plurality of cores obtained by punching a magnetic steel sheet into an annular shape into a cylindrical shape. A plurality of core plates are fixed to each other so as not to be separated from each other. The core plates are fixed to each other by welding, bolting, caulking, or the like. Japanese Patent No. 3550971 (Patent Document 1) discloses a stator core in which core plates of a magnetic steel sheet are fixed to each other at fixation portions provided at a plurality of locations in the circumferential direction.
In providing such fixation portions, if welding grooves, bolt holes, or the like are formed in the core plates, the magnetic path in the stator core is accordingly reduced. In addition, in the case where the core plates are deformed by caulking, the magnetic properties may be varied by the deformation to reduce the effective magnetic path. Here, when the rotor having the permanent magnets relatively rotates with respect to the stator and magnetic flux passes through the fixation portions, torque of the rotor may be fluctuated in correspondence with the fixation portions. If the pitch angle of the fixation portions in the stator core is an integer number of times the pitch angle of the permanent magnets (the pitch angle of the magnetic poles) in the rotor, a plurality of magnetic poles pass through a plurality of fixation portions at the same time periodically, which increases torque fluctuations. Therefore, Patent Document 1 proposes setting an inter-fixation portion angle (α) between the fixation portions to an angle that is not an integer number of times the pitch angle (A) of the magnetic poles (Patent Document 1; the third to tenth paragraphs etc.).
In addition, the thickness of the magnetic steel sheet as the material of the core plates is not completely uniform. Therefore, if the core plates are stacked in such an attitude that a reference direction determined with respect to the magnetic steel sheet is aligned in the same direction, errors in thickness of the magnetic steel sheet may be accumulated so that the total thickness of the plurality of core plates may significantly differ among positions in the circumferential direction of the stator core. Therefore, in general, rotational buildup in which the core plates are stacked while being rotated in the circumferential direction is performed to make the total thickness of the plurality of core plates uniform at various positions in the circumferential direction. A plurality of fixation portions is included in the range of rotational angle in the circumferential direction for rotational buildup. In Patent Document 1, such fixation portions are referred to as a fixation portion set. Then, the rotational angle in the circumferential direction for rotational buildup is referred to as an inter-fixation portion set angle (β). Patent Document 1 further proposes setting the inter-fixation portion set angle (β) to an angle that is not an integer number of times the pitch angle (A) of the magnetic poles (Patent Document 1; the eleventh paragraph etc.).
In order to fix the stator core, caulking which can shorten the lead time compared to welding and also can suppress the cost of manufacture is often applied. It should be noted, however, that caulking generally provides a small fastening force compared to welding. Therefore, it is necessary to set a large number of fixation portions compared to a case where welding is adopted. If the number of fixation portions is increased, the number of times when the magnetic poles and the fixation portions are arranged in one line along the radial direction of the rotary electric machine is also increased. Patent Document 1 provides countermeasures for a case where the number of fixation portions is smaller than the number of magnetic poles, and does not mention a case where the number of fixation portions is larger than the number of magnetic poles. In addition, Patent Document 1 prescribes the relationship between the pitch angle (A) of the magnetic poles and the inter-fixation portion angle (α) and the relationship between the pitch angle (A) of the magnetic poles and the inter-fixation portion set angle (β), but does not necessarily quantitatively prescribe the comprehensive relationship among (A, α, β). Thus, there is desired a technique that is widely applicable to a variety of types of rotary electric machines.